1. Field of the Invention
The present invention relates generally to a displacement hull ship provided with hydrofoils to raise the ship in the water during cruising to reduce wetted surface area.
2. Prior Art
Proposals have been made to equip ships of various configurations with hydrofoils. Many of these proposals mount the hydrofoils on struts which depend a substantial distance beneath the hull. When the ship is underway, the hydrofoils cause the hull to rise above the surface of the water. Supporting the hull above the water creates stability problems and subjects the bottom of the hull to wave pounding. Ships of this type are limited to use in inland and near coastal waters where high waves and choppy seas are not encountered. Since the hull is elevated fully out of the water during cruising, the load carrying capacity of such ships is limited by the lift obtainable from the hydrofoils.
Proposals have been made to use hydrofoils on submarines to draw the submarine under water and to guide its ascent and descent while submerged. Proposals have also been made to use hydrofoils on displacement ships as an aid to steering and to help control pitch. In such ship installations, steering control is facilitated by the ejection of fluids through openings in the hydrofoil surfaces.
3. The Parent Case
The referenced parent patent describes a displacement hull ship provided with submerged hydrofoils to raise the hull in the water when the ship is underway. The hull is not raised out of the water during cruising, but rather is raised a sufficient amount to substantially reduce wetted surface area and attendant drag forces.
A significant feature of the described ship is the cross-section of the hull. The sides of the hull are described as having upper, lower and intermediate portions. The upper portions are relatively widely spaced and described as extending substantially vertically. The lower portions are relatively narrowly spaced and described as extending substantially vertically. The intermediate portions form inclined transition surfaces between the upper and lower portions.
When the described ship is at rest in the water, the displacement water line is near the juncture of the upper and intermediate portions. At this time, a substantial portion of the hull is submerged and the ship is wholly supported by displacement forces.
When the described ship is cruising, lift forces derived from the hydrofoils lift the hull such that the crusing water line is near the juncture of the lower and intermediate portions. At this time, a substantial portion of the hull is still submerged and displacement forces still contribute significantly to the support of the ship; but the relatively large surface area of the inclined intermediate portions is now out of the water. The resulting decreases in wetted surface area substantially reduces drag and permits increased operating speeds with a savings in fuel consumption.
Raising the hull in the water by "X" linear units will reduce the wetted hull surface by "X" times the secant of the angle by which the sides are inclined from the vertical. By substantially confining the inclined portions of the sides to the region of the hull which rises out of the water, the angle of side inclination can be selected to maximize the amount of wetted surface area that will be removed from the water with each linear unit of rise of the hull.
A desirable angle of inclination of the intermediate side portions is within the range of 35.degree.-55.degree.. This range of angles provides the intermediate side portions with a sufficient angle of inclination to dissipate the impact of wave pounding, and yet provides a secant of within the approximate range of 1.2 to 1.7 which, as was previously explained, will effect a rapid reduction of the wetted hull surface as the ship gets underway.
The hydrofoils of the described ship are supported on the submerged keel section of the hull. The hydrofoils preferably do not protrude beyond the maximum width of the deck of the ship, thereby enabling the ship to use conventional docking facilities. The hydrofoils are preferably movably mounted so that the front portion of each foil can be elevated relative to its rear portion to increase lift, or lowered relative to its rear portion to decrease lift.
Another feature of the described ship lies in the positioning of the foils in groups so that the hydrofoils of each group can provide substantially a contiguous surface to raise the hull as the ship gets underway. The adjacent foils of each group are arranged in close proximity to each other with the forward foils positioned higher than their adjacent rearward foils. By this arrangement, the foils can be rotated to a position of alignment wherein the adjacent foils provide continuous high-lift surfaces on each side of the ship to increase lift and decrease the amount of time needed to reach cruising speed and attitude.
It is estimated that the described ship can be used to transport cargo at approximately 20 knots on the same amount of fuel used by conventional displacement hull ships in attaining between 12 and 15 knots of speed. Estimates are that 30 knots of speed are attainable for a 20-knot fuel bill. Accordingly, greater economies are found in high-speed operation than are available to conventional ships.
The advantages of the described hull cross-section accordingly include:
1. A deep-submergence hull is provided which does not raise the hull out of the water and accordingly does not subject the bottom of the hull to wave pounding. PA1 2. A minimal wetted surface area is held in the water, thereby minimizing drag. PA1 3. A stable cargo-supporting platform is provided by the deep-submergence hull which is subject to minimal pitch in choppy seas. PA1 4. Since the submerged keel section is of relatively small cross-section, it can easily be rigidly braced to withstand high impact loads. PA1 5. The slim cross-section of the submerged keel section permits the use of relatively long hydrofoils along opposite sides without causing these hydrofoils to extend beyond the maximum width of the cargo-carrying deck.
Still another feature of the described hull cross-section is that it can be increased or decreased in scale to provide larger or smaller ships.